1. Field of the Invention
The present invention relates to an updating or restoring method for stored data groups and a system for executing the same, wherein when the updating of the data group stored in a nonvolatile storage device fails, the data group can be restored with consistency.
2. Description of the Related Art
In a data processing system, a nonvolatile storage device is used wherein if a main power supply of the system fails, stored information is protected by a battery back up or some other means. The above nonvolatile storage device can be accessed by an instruction which is used for accessing a main storage device instead of an instruction applied to an input or output device. As a result, the nonvolatile storage device can be accessed or updated at high speed. A data updating or restoring system suitable for the above nonvolatile storage device is desired.
As an updating system for use when a failure during an updating process occurs the following two systems have been utilized.
First system:
The data before updating is temporarily transferred to another storage device or the like, and after that the original data is updated. The temporarily transferred data is referred to as a pre-update log. When an updating process is interrupted by a failure, the data lost by the interruption is taken from the pre-update log and restored.
Second system:
First, the new data to be updated is temporarily stored in another storage device or the like, and the data to be updated is then updated. The temporarily stored data is referred to as a post-update log. When an updating process is interrupted by a failure, the data is updated again using the post update log.
In the above conventional systems, either the pre-update log or post-update log must be stored in another storage device or the like in advance. Thus, when the data is updated, an excessive number of write operations are necessary to store the log data. Also, in the restoring process after interruption of the updating, the stored data must be read and transferred to the data domain to be updated again. Accordingly, a long time is necessary to carry out the updating process as well as the restoring process because of the necessity of writing and reading the data. As a result, problems arise.